HitTestSystem.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Unity.Physics;
using Unity.Mathematics;
using Unity.Transforms;
using Unity.Entities;
using Unity.Physics.Systems;

[AlwaysUpdateSystem]
public class HitTestSystem : ComponentSystem
{
    BuildPhysicsWorld m_BuildPhysicsWorldSystem;
    StepPhysicsWorld m_StepPhysicsWorldSystem;

    protected override void OnCreateManager()
    {
        m_BuildPhysicsWorldSystem = World.GetOrCreateManager<BuildPhysicsWorld>();
        m_StepPhysicsWorldSystem = World.GetOrCreateManager<StepPhysicsWorld>();
    }

    protected override void OnUpdate()
    {
        foreach(var contactEvent in m_StepPhysicsWorldSystem.Simulation.CollisionEvents)
        {
            var physicsWorld = m_BuildPhysicsWorldSystem.PhysicsWorld;

            var bodyA = physicsWorld.Bodies[contactEvent.BodyIndices.BodyAIndex];
            var bodyB = physicsWorld.Bodies[contactEvent.BodyIndices.BodyBIndex];

            PostUpdateCommands.DestroyEntity(bodyA.Entity);
        }
    }
}